Electric contact apparatus



Ap 7, 1942-v J. GoER-rH I ELECTRIC CONTACT APPARATUS Filed Nov. 18, 1939 MERCI/IY k gni/griffig INvE MC1/MM BY WTQRNEY Patented Apr. 7, 1942 Johannes Goerth, Berlin-Grunewald, Germany, assignor to Siemens Apparate und Maschinen Gesellschaft mit beschrnkter Haftung, Berlin, Germany, a corporation of Germany Application November is, 1939, serial No. 305,185

1n Germany November 30, 1938 6 Claims.

This invention relates to electric contact apparatus, and more particularly to sliding contact apparatus for use in measuring instruments having a low directive force.

Devices have heretofore been provided of this character having a stationary contact member which is in engagement with a movable contact member. In order to insure an undisturbed V4iiow of current in the circuit in which the contact device is connected there is required a certain minimum contact pressure between the two members. However, this pressure produces a certain amount of friction which has a very disadvantageous effect, particularly when the contact device is used with measuring instruments, the indicator of which is moved by a low torque. The above mentioned friction causes an undesirable braking action and thereby causes inaccurate readings of the indicator. Additional error is produced by overcoming the resistance to motion of the movable contact member when the latter begins its movement.

One of the objects of the present invention is to provide a contact device having novel contact arms, the friction between said arms being reduced to a minimum.

Another object of the invention is to provide a novel contact device which does not interfere with the accurate operation of apparatus with which it is associated.

A further object is to provide a novel structure of the above character having a high electric conductivity but a low friction between the moving parts thereof.

The above and further objects and novel features will more fully appear from the detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for purposes of illustration only and is not intended as a definition of the limits ofthe invention, reference for this latter purpose being had primarily to the appended claims.

In the drawing, wherein like reference characters refer to like parts throughout the several views,

Fig. 1 is an isometric view partly in section of one embodiment of the invention;

Fig. 2 is aside elevation with the cover removed of the embodiment shown in Fig. 1;

Fig. 3 is a detailed view partly in section and with parts broken away of a portion of a cony tact arm shown in Figs. 1 and 2;

Fig. 4 is a detailed view partly in section of a modification of a contact arm which may be employed in the ilrst embodiment;

Fig. 5 is a detailed view partly in section and with parts broken away of a contact arm constituting a second embodiment of the invention;

and

Fig. 6 is a .detailed view partly in section of a modification of the embodiment of Fig. 5.

The forms of the invention illustrated in the accompanying drawing, by way 4of example, comprise an eiectricity conducting contact device which is employed in combination with a measuring instrument. The contact apparatus is constituted by a fixed contact member adjacentA which a second contact member is movable. A globule or drop of mercury is mounted on one of the two contact members in such a manner that it cannot escape therefrom, and in such a manner that it remains in contact with the other oi said members. Means are provided to assure a uniform and even pressure of the contacting mercury drop against the contact member which cooperates with the member on which the drop is mounted.

In the forms shown and in Figs. 1 and 2. an electric measuring instrument, for example, an ammeter or a voltmeter Il is employed with the novel contact device, the instrument having a coil ii upon a core i2 which is movable in the iield of magnets i3; The core I2 is pivotally mounted upon a shaft IZa and is maintained in a predetermined position by opposed coil springs i4 which are preferably mounted adjacent the extremities of said shaft. The shaft i2a may be provided with a conventional pointei` at one end thereof passing over a conventional scale or dialgenerally shown in Figure 1.

In order that the measuring instrument may control, for example, a group of relays in response tomovements of the core of the instrument from a predetermined position, the novel contact apparatus is provided comprising a primary contact member or arm I5 which is operatively connected to the shaft |2a and, in the form shown, is rigidly attached thereto. Arm l5 is movable adjacent a second contact member i6, for example, a coil resistance. A circuit in which the above mentioned relays are connected is constituted, for example, by leads i1 and il which are connected to opposite extremities of the resistance i8 and are also connected to suitable relays AI9 and 20 respectively. The relays are interconnected by a lead 2i which, 'through an electric power source 22'and a suitable brush and slip-ring device 23, is connected to the contact arm Il.

The arm I5 is not in frictional contact with member I4 but is in electrical contact therewith by means of a drop or globule of mercury 24 which is mounted, in the form shown, in the rlower extremity of arm i5. In Fig. 3, there is shown on a large scale the extremity of the movable arm, there being provided therein a heini spherical recess 25 for the reception of the mercury drop. A suitable cap member 26 is provided for the arm for retaining the drop in position, the cap having a perforation 26a therein which is in register with the recess 25 and which conforms to the spherical shape thereof. The outer portion of said perforation is consequently provided with lips 21 which retain the mercury drop. The cap 2B vis preferablyremovably secured to the contact arm in order to permit a replacement oi' the mercury globule.

Fig. 4 illustrates a modiilcation of the mercury drop mounting means and comprises a cap which is similar to the one above described and which ls mounted upon a contact arm having no hemlspherical recess therein. A mercury drop in the cap recess consequently will have a flattened surface which rests against the transverse cross-section of the contact arm, the mercury drop approximating a hemisphere in shape.

A contact element comprising a second embodiment of the invention is shown in Fig. 5, which is constituted by a contact arm 23 which externally appears similar to the contact arm I3. However, the arm 28 is provided with a longitudinal bore 29 therein in which suitable means are mounted for exerting a pressure upon the globule of mercury 24 at the outerextremity of the arm. Inwardly extending lips 28a are provided for preventing the mercury drop from escaping from 'the bore 29, the means for exerting the pressure against the mercury comprise, in the form shown, a piston member 30 having a preferably cup-shaped member 30a at one extremity thereof in which rests the mercury. Resilient means comprising a spring 3| urges the piston 30 axially toward the drop of mercury, the spring being retained by a ring element 32, which is` secured within the bore 29 in such a position that the spring 3| is under compression.

A modiiication of the embodiment shown in Fig. 5 is illustrated in Fig. 6 having a contact arm 2l, and av piston 30, which are similar to those previously described. However, instead of urging the piston 30 against the mercury by means of a spring, the piston is axially urged toward the mercury by means of a magnet 33 which may be either a permanent or an electromagnet. The member 33 is preferably circular and surrounds arm 23 adjacent the extremity thereof within the desired limits of motion of the piston 30.

In order to make the mercury drop 24 shockproof, for example, against sudden vibrations oi the potentiometer system, which vibrations may cause a shattering of the drop, the distance between the extremity of member I5 and member I6 is very small, i e., said members are relatively movable closely adjacent one another but are not in irictional contact,

In order to prevent a chemical combination of the mercury drop 24 with the oxygen of the surrounding air, the contact' arrangement is mounted within a suitable container 34, which is filled with a chemically suitable fluid such as nitrogen or a light mineral oil.

In operation, as arm I5 moves from its predetermined position relative to resistance Il which,'in the form shown, is in the center oi the resistance, there is no frictional contact between said members but there is a highly eilicient electricalcontact therebetween provided by the mercury particle 24 which is retained by arm l5 and which substantially, frictionlessly slides over the resistance i6. The relays i9 and 2l, by suitable means not shown, can control associated apparatus, and are actuated in a conventional manner as the two contact members relatively move from their predetermined initial positions.

There is thus provided novelmeans for enabling a device, having a small directive force, to control the position of one electric contact member relative to another, the control being accomplished substantially without friction, there being' a highly elclent current conducting means therebetween. The novel means are extremely inexpensive to manufacture and very simple to construct. Furthermore, the device is adapted for withstanding violent vibrations and is well adapted for use in vehicles such as aircraft.

Although only two embodiments of the present invention have been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. For example, the electric circuit, illustrated in Fig. 2, may be replaced by any suitable circuit wherein a current flowing therein is responsive to the relative movements of the contact members. Also it is possible to form the surface of the member I6 against which mercury drop 24 moves in the shape of a groove, the contact drop sliding in said groove. Various changes may be made in the design and arrangement of the parts without departing from the spirit and scope of the invention as same will now be understood by those skilled in the art. For a definition of the limits of the invention, reference may be had to the appended claims.

What is claimed is:

l. An electrical contact member comprising a hollow cylindrical arm, a globule of mercury mounted within said hollow arm at one end thereof and having a portion thereof projecting from said arm, a retaining lip for holding said globule of mercury to said arm, and a yieldably urged piston within said arm for urging said globule of mercury against said retaining lip.

2. An electrical Contact member comprising a hollow cylindrical arm, a globule of mercury mounted within said hollow arm at one end thereof and having a portion thereof projecting from said arm, a retaining lip for holding said globule of mercury to said arm, an axially movable piston within said arm, and a resilient member within said arm for axially moving said piston within. said arm toward said globule of mercury whereby the latter is urged against said retaining lip.

3. An electrical contact member comprising a recessed cylindrical arm, a globule of mercury mounted upon said arm within said recess, a retaining lip for holding said globule of mercury upon said arm, and a magnetic member associated with said arm for urging said globule of mercury against said retaining lip.

4. An electrical contact `member comprising a cylindrical arm having a passage therein, a globule of mercury mounted within said passage and having a portion thereof projecting from said arm, a retaining lip for holding said globule of mercury within said passage, an axially movable piston within said passage, and a coiled member within said passage for yieldingly moving said piston axially toward said globule of mercury whereby the latter is urged against said retaining lip.

5. An electricalv contact member comprising a cylindrical arm having a passage therein, a globule of mercury mounted within said passage and having a portion thereof projecting from said arm, a retaining lip for holding said globule of mercury within said passage, an axially movable piston within said passage, a cup-shaped member carried by said piston at one end thereof for supporting a second portion of said globule of mercury therein, and resilient means within said passage for yieldingly urging said piston integral with said piston for supporting a second portion of said globule oi' mercury therein, and resilient means within said passage for yieldingly urging said piston and cup-shaped member, axially whereby said globule of mercury is urged and held against said retaining lip.

. JOHANNES GOERTH 

